Zoom lens and image capturing apparatus

ABSTRACT

There is provided a zoom lens including in order from an object side to an image side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power. In zooming from a wide-angle end to a telescopic end, the first lens group moves to the object side in a manner that a distance toward the second lens group narrows, and a distance between the third lens group and the fourth lens group widens. The third lens group includes a single lens or a single cemented lens.

BACKGROUND

The present technology relates to a zoom lens used for an imagecapturing apparatus, and specifically, relates to a zoom lens which isused for image capturing apparatuses such as a digital video camera anda digital still camera and which is small in dimensions and is large indiameter and an image capturing apparatus using the zoom lens.

Digital video cameras, digital still cameras and the like using asolid-state image sensor such as a CCD (Charge Coupled Device) and CMOS(Complementary Metal-Oxide Semiconductor) are rapidly spreading recentyears. Such spread of the digital cameras and the like leads to agrowing request for a zoom lens which is small in dimensions and largein diameter and which is excellent in portability and operable for alarge number of pixels. In view of such a request, cameras mounting azoom lens that is small in dimensions and large in diameter areincreasing especially. As such a zoom lens, there has been typicallyknown a zoom lens including four lens groups of a negative lens, apositive lens, a negative lens and a positive lens and having zoommagnifications of approximately 3 to 8 (for example, see Japanese PatentLaid-Open No. 2001-343584).

SUMMARY

In the above-mentioned existing technology reduces the size of the lensin dimensions with four lens groups of a negative lens, a positive lens,a negative lens and a positive lens, and has a magnification factor ofapproximately 3. The existing technology, however, has a risk that azoom lens that is far larger in diameter has to include, especially,huge second lens group and third lens group. Moreover, the existingtechnology is difficult to prevent a third lens group that is large indimensions in case of securing an efficient amount of light down to thefour corners of the screen since the spacing between the second lensgroup and third lens group is large in varying magnification. Moreover,in a manner in which vibration isolation is performed by moving the lensperpendicular to the optical axis, a zoom lens that is larger indiameter causes a larger vibration isolation group and larger drivingcomponents thereof, this leading to difficulty of attaining a smallerlens barrel as a whole.

It is desirable to provide a zoom lens which is compact in dimensionsand large in diameter and which still attains excellent opticalperformance over the whole zooming range.

According to an embodiment of the present technology, there is provideda zoom lens including, in order from an object side to an image side, afirst lens group having negative refractive power, a second lens grouphaving positive refractive power, a third lens group having negativerefractive power, and a fourth lens group having positive refractivepower. In zooming from a wide-angle end to a telescopic end, the firstlens group moves to the object side in a manner that a distance towardthe second lens group narrows, and a distance between the third lensgroup and the fourth lens group widens. The third lens group includes asingle lens or a single cemented lens.

The following conditional expressions (a) and (b) are satisfied,Δm3/(fw×ft)^(1/2)<0.3  conditional expression (a):d23_max/(fw×ft)^(1/2)<0.5  conditional expression (b):

where

-   -   Δm3 represents a variation amount of a distance between the        second lens group and the third lens group in varying        magnification, and d23_max represents a maximum value of the        distance between the second lens group and the third lens group        in varying magnification.

The lens includes four lens groups and satisfies the conditionalexpressions (a) and (b), reducing the whole optical length, and thus,attaining the zoom lens that is small in dimensions. Moreover,satisfying the conditional expressions (a) and (b) enables to attain thezoom lens that is small in dimensions, to keep an amount of light on theedges at an arbitrary zoom position large, and to realize highperformance.

Moreover, in the first aspect, the second lens group may include, inorder from the object side, four lenses of a first positive lens, asecond positive lens, a negative lens and a third positive lens. Thesecond positive lens and the negative lens are joined with each other.Such a configuration of the second lens group enables to reduce thewhole optical lengths at the wide-angle end and at the telescopic end.Moreover, the first positive lens may be a positive single lens and thesecond positive lens and the negative lens may be joined with eachother, this enabling to suppress the thickness of the second lens groupin the optical axis direction with the positive power of the second lensgroup kept high.

Moreover, in the first aspect, the third lens group may satisfy thefollowing conditional expression (c),−3<f3g/ft<−0.8  conditional expression (c):

where

-   -   f3g represents a focal length of the third lens group, and ft        represents a system focal length at the telescopic end. When        excess over the upper limit in the conditional expression (c)        takes place, the power of the third lens group is too high, this        resulting in difficulty of maintaining performance due to        assembly errors in production. Moreover, when shortage to the        lower limit in the conditional expression (c) takes place, the        power of the third lens group is too low, this causing the whole        optical length to lengthen and the zoom lens to be difficult to        be small in dimensions.

Moreover, in the first aspect, vibration isolation may be performed bymoving the third positive lens or the third lens group perpendicularlyto an optical axis. The third positive lens or the third lens group,which is disposed behind the second lens group having the positive power(at the portion where the light rays are most concentrated), may be thevibration isolation group, this attaining the vibration isolation groupand vibration isolation driving part to be small in dimensions and thewhole lens barrel to be small in dimensions.

Moreover, in the first aspect, the zoom lens may include an aperturestop disposed on the second lens group or between the second lens groupand the third lens group, and a light shielding member shielding acircumferential light ray on a part of the third lens group at thewide-angle end. The following conditional expression (d) may besatisfied,L×Fno _(—) w/(fw×ft)^(1/2)<2.5  conditional expression (d):

where

-   -   L represents a distance along an optical axis between the        aperture stop and the light shielding member at the wide-angle        end, Fno_w represents an F value at the wide-angle end, fw        represents a system focal length at the wide-angle end, and ft        represents a system focal length at the telescopic end. The        aperture stop defining the F value may be disposed on the second        lens group or the third lens group whose effective passing range        of the light rays is narrower than those of the first lens group        and fourth lens group, this attaining the aperture stop to be        small in dimensions and be light. Furthermore, the        circumferential light rays at the wide-angle end may be shielded        on a part of the third lens group where the circumferential        light rays are more separated from the F value light rays        compared with the second lens group, this attaining the zoom        lens that is large in diameter and the harmful light in the        circumference of the screen to be cut effectively.

Moreover, in the first aspect, each of the third positive lens and thethird lens group includes a single lens made of a resin. The third lensgroup relatively low in power may be a single lens made of a resin, thissuppressing chromatic aberration from arising relatively and attainingthe lens that is light. Furthermore, the third positive lens or thethird lens group that is the single lens made of a resin may be thevibration isolation group, this attaining the vibration isolation groupthat is light and the vibration isolation driving components that issmall in dimensions, and thus, attaining the whole lens barrel that issmall in dimensions.

According to a second embodiment of the present technology, there isprovided an image capturing apparatus including a zoom lens including,in order from an object side to an image side, a first lens group havingnegative refractive power, a second lens group having positiverefractive power, a third lens group having negative refractive power,and a fourth lens group having positive refractive power, and an imagesensor converting an optical image formed by the zoom lens into anelectric signal. In zooming from a wide-angle end to a telescopic end,the first lens group moves to the object side in a manner that adistance toward the second lens group narrows, and a distance betweenthe third lens group and the fourth lens group widens. The third lensgroup includes a single lens or a single cemented lens, and theabove-described conditional expressions (a) and (b) are satisfied.

The present technology has the effects of being compact in dimension andlarge in diameter and still attaining excellent optical performance overthe whole zooming range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a lens configuration of a zoom lensaccording to a first embodiment of the present technology;

FIG. 2 illustrates aberration of the zoom lens according to the firstembodiment of the present technology at the wide-angle end at infinityfocus;

FIG. 3 illustrates aberration of the zoom lens according to the firstembodiment of the present technology at the intermediate focal length atinfinity focus;

FIG. 4 illustrates aberration of the zoom lens according to the firstembodiment of the present technology at the telescopic end at infinityfocus;

FIG. 5 is a diagram illustrating a lens configuration of a zoom lensaccording to a second embodiment of the present technology;

FIG. 6 illustrates aberration of the zoom lens according to the secondembodiment of the present technology at the wide-angle end at infinityfocus;

FIG. 7 illustrates aberration of the zoom lens according to the secondembodiment of the present technology at the intermediate focal length atinfinity focus;

FIG. 8 illustrates aberration of the zoom lens according to the secondembodiment of the present technology at the telescopic end at infinityfocus;

FIG. 9 is a diagram illustrating a lens configuration of a zoom lensaccording to a third embodiment of the present technology;

FIG. 10 illustrates aberration of the zoom lens according to the thirdembodiment of the present technology at the wide-angle end at infinityfocus;

FIG. 11 illustrates aberration of the zoom lens according to the thirdembodiment of the present technology at the intermediate focal length atinfinity focus;

FIG. 12 illustrates aberration of the zoom lens according to the thirdembodiment of the present technology at the telescopic end at infinityfocus; and

FIG. 13 is a diagram illustrating an image capturing apparatus 100 towhich any of the zoom lenses according to the first to third embodimentsof the present technology is applied.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

A zoom lens according to the present disclosure includes: in order froman object side to an image side, a first lens group having negativerefractive power; a second lens group having positive refractive power;a third lens group having negative refractive power; and a fourth lensgroup having positive refractive power. In zooming from a wide-angle endto a telescopic end, the first lens group moves to the object side suchthat a distance toward the second lens group narrows, and a distancebetween the third lens group and the fourth lens group widens. The thirdlens group includes a single lens or a single cemented lens. Such aconfiguration enables to enhance a zooming effect of the second lensgroup and third lens group and to reduce the whole optical length,without enhancing the power of the second lens group too much.

Furthermore, the zoom lens according to the present disclosure satisfiesthe following conditional expressions (a) and (b):Δm3/(fw×ft)^(1/2)<0.3  conditional expression (a):d23_max/(fw×ft)^(1/2)<0.5  conditional expression (b):

where Δm3 is a variation amount of a distance between the second lensgroup and the third lens group in varying magnification, and d23_max isa maximum value of the distance between the second lens group and thethird lens group in varying magnification.

The conditional expression (a) is an expression for defining the ratioof the variation amount of the distance between the second lens groupand third lens group in varying magnification relative to the squareroot of the product of the focal lengths at the wide-angle end and atthe telescopic end. When excess over the upper limit in the conditionalexpression (a) takes place, the variation amount of the distance betweenthe second lens group and third lens group is large relative to thefocal lengths at the wide-angle end and at the telescopic end, and therelative movement amount of the third lens group relative to the secondlens group is large, this causing the optical system to be difficult tobe small in dimensions. Moreover, securing a sufficient amount of lighton the edges at an arbitrary zoom position in varying magnificationcauses the zoom lens to be difficult to be small in dimensions.Accordingly, the zoom lens that satisfies the conditional expression (a)enables to suppress the variation amount of the distance between thesecond lens group and third lens group due to the zooming to suppress adecline of the amount of light on the edges and to be small indimensions.

The conditional expression (b) is an expression for defining the ratioof the maximum value of the distance between the second lens group andthird lens group in varying magnification relative to the square root ofthe product of the focal lengths at the wide-angle end and at thetelescopic end. Namely, the conditional expression (b) is an expressionfor securing the amount of light on the edges and making the third lensgroup small in dimensions. When excess over the upper limit in theconditional expression (b) takes place, the distance between the thirdlens group and second lens group is large, this causing the third lensgroup to be difficult to be small in dimensions and small in diameter.

In addition, the zoom lens according to the present disclosure ispreferable to satisfy the following conditional expressions (a′) and(b′):Δm3/(fw×ft)^(1/2)<0.2  conditional expression (a′):d23_max/(fw×ft)^(1/2)<0.3  conditional expression (b′):

Furthermore, in the zoom lens according to the present disclosure, thesecond lens group is desirable to include, in order from the objectside, four lenses of a first positive lens, a second positive lens, anegative lens and a third positive lens, and the second positive lensand the negative lens is desirable to be joined with each other. Such aconfiguration of the second lens group enables to give the second lensgroup high positive power and to reduce the whole length of the opticalsystem. Moreover, the first positive lens may be a positive single lensand the second positive lens and the negative lens may be joined witheach other, this enabling to suppress the thickness of the second lensgroup in the optical axis direction with the positive power of thesecond lens group kept high. Moreover, the second positive lens and thenegative lens may be a cemented lens obtained by joining them with eachother, this enabling to reduce sensitivity to production errors and toimprove ease of assembly.

Furthermore, the zoom lens according to the present disclosure isdesirable to satisfy the following conditional expression (c):−3<f3g/ft<−0.8  conditional expression (c):

where f3g is a focal length of the third lens group, and ft is a systemfocal length at the telescopic end.

The conditional expression (c) is an expression for defining the ratioof the focal length of the third lens group relative to the focal lengthof the whole lens system at the telescopic end. When excess over theupper limit in the conditional expression (c) takes place, the power ofthe third lens group is too high relative to the focal length at thetelescopic end, this resulting in high sensitivity to assembly errors ofthe second lens group and third lens group and causing deterioration ofperformance in production. Meanwhile, when shortage to the lower limitin the conditional expression (c) takes place, the power of the thirdlens group is too low, this causing the distance between the second lensgroup and third lens group in varying magnification to be difficult tobe suppressed. Moreover, suppressing the whole optical length causes thepower of the second lens group to be too high, this increasingsensitivity to errors in assembly and causing deterioration ofperformance.

In addition, the zoom lens according to the present disclosure is stillpreferable to satisfy the following conditional expression (c′):−2<f3g/ft<−0.85  conditional expression (c′):

Moreover, in the zoom lens according to the present disclosure, it isdesirable that vibration isolation is performed by moving the thirdpositive lens or the third lens group perpendicular to an optical axis.The third positive lens or the third lens group, which is disposedbehind the second lens group having the positive power (at the portionwhere the light rays are most concentrated among the portions of thegroups), may be the vibration isolation group, this enabling thevibration isolation group and vibration isolation driving part to besmall in dimensions and the whole lens barrel to be small in dimensionsand small in diameter. In particular, the third lens group may furthersatisfy the conditional expression (c), this enabling the stroke of thevibration isolation to be suitable and not too large and enabling it tobe compatible with suppression of deterioration of performance in thevibration isolation.

Furthermore, in the zoom lens according to the present disclosure, it isdesirable that an aperture stop defining the F value is disposed on thesecond lens group or the third lens group, that a circumferential lightray is shielded on a part of the third lens group at the wide-angle end,and that the following conditional expression (d) is satisfied:L×Fno _(—) w/(fw×ft)^(1/2)<2.5  conditional expression (d):

where L is a distance along an optical axis between the aperture stopand the light shielding member at the wide-angle end, Fno_w is an Fvalue at the wide-angle end, fw is a system focal length at thewide-angle end, and ft is a system focal length at the telescopic end.

The aperture stop defining the F value may be disposed on the secondlens group or the third lens group whose effective passing range of thelight rays is narrower than those of the first lens group and fourthlens group, this enabling the aperture stop to be small in dimensionsand be light. Furthermore, it is more desirable to dispose the aperturestop defining the F value in front of the second lens group and toshield the circumferential light rays at the wide-angle end behind thethird lens group. Separating the aperture stop regulating the F valuelight rays from the light shielding part of the circumferential lightrays along the optical axis as far as possible enables the lens that islarge in diameter to shield the light rays effectively at the positionwhere the light rays along the axis are separated from the light raysoff the axis (at the position away from the optical axis on the F valueaperture stop), this enabling the zoom lens to be small in dimensionsand high in performance compatibly.

When excess over the upper limit in the conditional expression (d) takesplace, the aperture stop defining the F value is too far from theposition of the light shielding part shielding the circumferential lightrays at the wide-angle end relative to the diameter, this causing thezoom lens that is large in diameter to be difficult to be compatiblewith being small in dimensions.

In addition, the zoom lens according to the present disclosure is stillpreferable to satisfy the following conditional expression (d′):L×Fno _(—) w/(fw×ft)^(1/2)<2  conditional expression (d′):

Furthermore, in the zoom lens according to the present disclosure, it isdesirable that each of the third positive lens and the third lens groupincludes a single lens made of a resin. The third lens group relativelylow in power may be a single lens made of a resin, this suppressingchromatic aberration from arising and enabling the lens to be light.Furthermore, the third positive lens and the third lens group each ofwhich is the single lens made of a resin may be the vibration isolationgroup, this enabling the vibration isolation group to be light and thevibration isolation driving components to be small in dimensions, andthus, enabling the whole lens barrel to be small in dimensions.

In the zoom lens according to the present disclosure, in order to secureits excellent optical performance and enable it to be wide-angle, highzooming and small in dimensions, the lens groups are desirable to beconfigured as follows.

Regarding the first lens group, it is desirable that the negative lensand the positive meniscus lens are disposed closest to the object sideand closest to the image side, respectively. The negative lens of thefirst lens group on its object side is desirable to employ, for example,glass material with a refractive index of 1.8 or more. The larger therefractive index is, the smaller the curvature of the first lens groupcan be, making the negative power of the first lens group high.Moreover, the positive meniscus lens on the object side that employs ameniscus lens convex to the object side makes an incident angle of lightoff the axis at the wide-angle end small, this enabling to suppressaberration off the axis from arising. Furthermore, the Abbe number ofthe positive meniscus lens is desirable to be 25 or less. The Abbenumber being 25 or less enables the refractive index of the negativelens on the object side to be 1.85 or more and the light flux along theaxis at the telescopic end to be suppressed effectively.

The second lens group is desirable to include, in order from the objectside, a positive single lens, a cemented lens including a positivesingle lens and a negative single lens, and a positive single lens.Disposing the positive single lenses on the object side and image sideof the second lens group enables to distribute the positive power of thesecond lens group thereon and to make the positive power high, thisenabling to reduce the whole length of the optical system. Moreover,disposing the cemented lens between the positive single lenses on theobject side and image side enables to suppress chromatic aberration andto suppress eccentric sensitivity in the second lens group, thisreducing sensitivity to production errors and improving ease ofassembly. Furthermore, making the positive single lens on the objectside non-spherical and disposing an F value aperture stop in itsvicinity enable to make the power of the second lens group high, and inaddition, to correct aberration (especially, spherical aberration),being still preferable.

The third lens group is desirable to include a negative cemented lens ora negative single lens, and further, to have a convex surface on theobject side and at least one non-spherical surface. The convex surfaceon the object side makes an incident angle of F value light incidentfrom the second lens group small, this enabling to correct aberration onthe axis effectively even for a lens that is large in dimension.Moreover, it is desirable to dispose the non-spherical surface at leaston the image side of the third lens group. Disposing the non-sphericalsurface on the image side of the third lens group far from the aperturestop defining the F value enables to correct aberration off the axiseffectively. Moreover, when the third lens group is the vibrationisolation group, disposing the non-spherical surface enables to suppressvariations of various kinds of aberration in vibration isolationeffectively. Furthermore, the negative single lens is desirable to havethe Abbe number of 50 or more in consideration of the chromaticaberration.

The fourth lens group is desirable to include a single lens and to beused, for example, for focusing. The fourth lens group that isconfigured of a single lens attains minimal load on the driving part intransportation and realizes the lens barrel which is small in dimensionsand is light.

In the zoom lens according to the embodiment of the present disclosure,shifting one lens group out of the first lens group to fourth lens groupor part of lenses in one lens group in the direction substantiallyperpendicular to the optical axis enables to shift the position of theimage. Specifically, the second lens group or the third lens group,which is low in height of the effective light rays, which group isconfigured as the vibration isolation group enables the vibrationisolation group to be small in dimensions and be light and its drivingsystem to be small in dimensions and be light, this leading to the lensbarrel that is small in dimensions. Moreover, the zoom lens in which theposition of the image can be shifted is desirable to be integrated witha detection system detecting image blur, a driving system shifting theindividual lens groups, and a control system giving the shift amount tothe driving system based on the output from the detection system,allowed to function as a vibration isolation optical system correctingcamera shake and image blur. Furthermore, in order to prevent moirefringe patterns from arising on the image side of the lens system, alow-pass filter may be disposed and an infrared light absorption filtermay be disposed according to spectroscopic sensitivity characteristicsof light receiving elements.

In the zoom lens according to the embodiment of the present disclosure,a negative lens high in power is disposed on the surface of incidence,tending to cause distortion aberration presenting barrel-shapeddistortion at the wide-angle end. Against this, it is desirable toemploy a function of changing image distortion by processing capturedimage data, and thus, to correct the image distortion caused by thedistortion aberration arising in the optical system for the observation.Moreover, deliberately allowing the barrel-shaped distortion to arisegives a low height of incident light at the wide-angle end compared withthe field of view, this enabling the diameter of the first lens group tobe small and the reflective members in the first lens group to be smallin dimensions, attaining further smaller ones.

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted. The description is made in the followingorder.

1. First Embodiment (Example 1 of Numerical Values)

2. Second Embodiment (Example 2 of Numerical Values)

3. Third Embodiment (Example 3 of Numerical Values)

4. Application Example (Image Capturing Apparatus)

Incidentally, signs and the like used in the following tables anddescriptions mean as follows. A “surface number” designates the ithsurface from the object side. A “curvature radius R” designates thecurvature radius of the ith surface from the object side. A “spacing Di”denotes the variable spacing with respect to the spacing between the ithsurface and the (i+1)th surface along the axis. Regarding the “surfacenumber”, “ASP” indicates that the surface is non-spherical. Regardingthe “curvature radius R”, “INFINITY” indicates that the surface isplanar. A “refractive index Nd” designates the refractive index of theglass material having the ith surface on its object side which index isto the d lines (wavelength of 587.6 nm). An “Abbe number Vd” designatesthe Abbe number of the glass material having the ith surface on itsobject side which number is to the d lines. The sign “f” denotes a focallength. The sign “Fno” denotes an F value (F number). The sign “ω”denotes a half FOV.

Moreover, some zoom lenses used in the individual embodiments havenon-spherical lens surfaces. Each of them is supposed to be defined asfollows:x=cy ²/(1+(1−(1+κ)c ² y ²)^(1/2))+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰

where the sign “x” denotes a distance from the vertex of the lenssurface in the optical axis direction (amount of sagging), the sign “y”denotes a height in the direction perpendicular to the optical axis, thesign “c” denotes a paraxial curvature at the lens vertex, and the sign“κ” denotes a conic constant. In addition, the numbers A4, A6, A8 andA10 denote fourth-order, sixth-order, eighth-order and tenth-ordernon-spherical coefficients.

1. First Embodiment Lens Configuration

FIG. 1 is a diagram illustrating a lens configuration of a zoom lensaccording to a first embodiment of the present technology. The zoom lensincludes, in order from the object side to the image side, a first lensgroup GR1 having negative refractive power, a second lens group GR2having positive refractive power, a third lens group GR3 having negativerefractive power and a fourth lens group GR4 having positive refractivepower. In each of this figure and other figures illustrating thefollowing lens configurations, the upper portion, middle portion andlower portion illustrate the lens positions at the wide-angle end, atthe intermediate focal length and at the telescopic end, respectively.As the focal length comes closer to that of the telescopic end from thatof the wide-angle end, the lenses locate at the positions indicated bythe arrows. The solid line arrows indicate the movements thereof inzooming.

The first lens group GR1 includes, in order from the object side to theimage side, a double convex-shaped negative lens L11 and ameniscus-shaped positive lens L12 convex to the object side.

The second lens group GR2 includes, in order from the object side to theimage side, a positive single lens L21 convex to the object side and acemented lens configured by joining a double convex-shaped positive lensL22, a double concave-shaped negative lens L23, and a doubleconvex-shaped positive lens L24.

The third lens group GR3 includes a meniscus-shaped negative lens L31convex to the object side.

The fourth lens group GR4 includes a double-convex positive lens L41.

In the zoom lens according to the first embodiment, an aperture stop STOis disposed on the object side of the second lens group GR2. Theaperture stop STO defines the F value. Moreover, a filter SG is disposedbetween the fourth lens group GR4 and an image plane IMG. Furthermore,with a mask pasted on the imaging surface (R2 surface) of the negativelens L31 of the third lens group GR3, light rays on the circumference atthe wide-angle end are shielded.

The zoom lens according to the first embodiment has a magnificationfactor of 3.2. In zooming, the first lens group GR1, second lens groupGR2, third lens group GR3 and fourth lens group GR4 are movable.

[Specifications of Zoom Lens]

Table 1 presents data of the lenses in Example 1, in which specificnumerical values are applied to the zoom lens according to the firstembodiment.

TABLE 1 Surface Curvature Refractive Abbe Number i Radius R Spacing DIndex Nd Number Vd  1(ASP) −149.9996 0.500 1.851348 40.1045  2(ASP)15.1043 4.030  3 21.6089 2.070 2.0027 19.317  4 38.0000 26.321  5INFINITY 0.000 Opening Aperture Stop  6(ASP) 11.8965 3.150 1.7737647.167  7(ASP) 116.1629 0.150  8 18.2361 3.770 1.83481 42.7207  9−33.8241 0.860 1.74901 26.3211 10 7.2814 2.100 11 16.8286 2.500 1.5360056.0000 12 −44.4056 0.700 13(ASP) 16.5926 2.250 1.592014 67.0227 14(ASP)8.598 4.820 15(ASP) 45.7058 3.500 1.592014 67.0227 16(ASP) −25.06274.844 17 INFINITY 0.300 1.516798 64.1983 18 INFINITY 0.150 19 INFINITY0.500 1.556708 58.5624 20 INFINITY 1.000 21 INFINITY 0.000

In the zoom lens according to the first embodiment, the both surfaces ofthe negative lens L11 of the first lens group GR1 (first surface andsecond surface), the both surfaces of the positive lens L21 of thesecond lens group GR2 (sixth surface and seventh surface), the bothsurfaces of the positive lens L31 of the third lens group GR3(thirteenth surface and fourteenth surface) and the both surfaces of thepositive lens L41 of the fourth lens group GR4 (fifteenth surface andsixteenth surface) are non-spherical. Table 2 presents the conicconstants κ and the fourth-order, sixth-order, eighth-order andtenth-order non-spherical coefficients A4, A6, A8 and A10 of thesesurfaces. In addition, in Table 2 and the following other tablespresenting non-spherical coefficients, the expression “E−i” is anexponential expression with a base of 10, that is, represents “10^(−i)”.For example, the expression “0.12345E−05” represents “0.12345×10^(−5”.)

TABLE 2 Surface Number κ A4 A6 A8 A10 1 0 −2.80742E−05  3.30306E−07−1.41743E−09 1.90007E−12 2 0 −4.09871E−05  1.31996E−07  1.20014E−09−1.21616E−11  6 0 −5.28855E−05  2.38601E−07 −1.01380E−08 1.98663E−10 7 05.04527E−06 5.76862E−07 −6.79844E−09 1.80657E−10 13 0 4.30359E−044.44756E−06  1.93761E−08 −3.60089E−10  14 0 6.52905E−04 6.14224E−06−1.16155E−07 6.36895E−10 15 0 1.49343E−05 −6.91862E−08  −1.54399E−097.67520E−12 16 0 5.89754E−05 −9.72308E−07   7.86103E−09 −2.95396E−11 

Table 3 presents the focal lengths f, F values Fno and half FOVs ω atthe wide-angle end, at the intermediate focal length and at thetelescopic end in Example 1.

TABLE 3 Wide-Angle Intermediate Telescopic End Focal Length End f 11.00419.634 35.424 Fno 1.855 3.399 5.065 ω 32.986 21.613 12.526

In the zoom lens according to the first embodiment, a spacing D4 betweenthe first lens group GR1 and second lens group GR2, a spacing D12between the second lens group GR2 and third lens group GR3, a spacingD14 between the third lens group GR3 and fourth lens group GR4 and aspacing D16 between the fourth lens group GR4 and filter SG vary inzooming between the wide-angle end and telescopic end. Table 4 presentsthe variable spacings with respect to the respective spacings at thewide-angle end, at the intermediate focal length and at the telescopicend in Example 1.

TABLE 4 Wide-Angle Intermediate Telescopic End Focal Length End f 11.00419.634 35.424 D4 26.321 10.613 2.750 D12 0.700 1.929 2.200 D14 4.82011.019 24.878 D16 4.844 4.609 3.632

[Aberration of Zoom Lens]

FIGS. 2 to 4 illustrate aberration diagrams of the zoom lens accordingto the first embodiment of the present technology at infinity focus.FIG. 2, FIG. 3 and FIG. 4 illustrate aberration diagrams at thewide-angle end, at the intermediate focal length and at the telescopicend, respectively. Portions a, portions b and portions c in thesefigures illustrate spherical aberration diagrams, field curvaturediagrams and distortion aberration diagrams, respectively.

In addition, in the spherical aberration diagrams, the solid lines,broken lines and dotted lines indicate values for the d lines (587.6nm), g lines (wavelength of 435.8 nm) and c lines (wavelength of 656.3nm). Moreover, in the astigmatism diagrams, the solid lines and dottedlines indicate values for the sagittal image surfaces and meridionalimage surfaces.

It is apparent from the aberration diagrams that Example 1 attainsexcellent imaging performance, correcting the aberrations favorably.

2. Second Embodiment Lens Configuration

FIG. 5 is a diagram illustrating a lens configuration of a zoom lensaccording to a second embodiment of the present technology. The zoomlens includes, in order from the object side to the image side, a firstlens group GR1 having negative refractive power, a second lens group GR2having positive refractive power, a third lens group GR3 having negativerefractive power and a fourth lens group GR4 having positive refractivepower.

The first lens group GR1 includes, in order from the object side to theimage side a double concave-shaped negative lens L11 concave to theobject side and a meniscus-shaped positive lens L12 convex to the objectside.

The second lens group GR2 includes, in order from the object side to theimage side, a positive single lens L21 convex to the object side, and acemented lens configured by joining a double convex-shaped positive lensL22, a double concave-shaped negative lens L23, and a doubleconvex-shaped positive lens L24.

The third lens group GR3 includes a meniscus-shaped negative lens L31convex to the object side.

The fourth lens group GR4 includes a double-convex positive lens L41.

In the zoom lens according to the second embodiment, an aperture stopSTO is disposed on the object side of the second lens group GR2. Theaperture stop STO defines the F value. Moreover, a filter SG is disposedbetween the fourth lens group GR4 and an image plane IMG. Furthermore,with a mask pasted on the imaging surface (R2 surface) of the negativelens L31 of the third lens group GR3, light rays on the circumference atthe wide-angle end are shielded.

The zoom lens according to the second embodiment has a magnificationfactor of 3.2. In zooming, the first lens group GR1, second lens groupGR2, third lens group GR3 and fourth lens group GR4 are movable.

[Specifications of Zoom Lens]

Table 5 presents data of the lenses in Example 2, in which specificnumerical values are applied to the zoom lens according to the secondembodiment.

TABLE 5 Surface Curvature Refractive Abbe Number i Radius R Spacing DIndex Nd Number Vd  1(ASP) −104.6241 0.500 1.851348 40.1045  2(ASP)15.6174 4.030  3 23.4091 2.070 2.0027 19.317  4 45.0000 26.096  5INFINITY 0.000 Opening Aperture Stop  6(ASP) 12.1036 3.150 1.7737647.167  7(ASP) 114.2156 0.100  8 16.6038 3.750 1.83481 42.7207  9−35.7469 0.860 1.74901 26.3211 10 7.1463 2.100 11 16.6769 2.500 1.5360056.0000 12 −45.5368 0.700 13(ASP) 16.5975 1.556 1.53600 56.0000 14(ASP)7.9469 5.210 15(ASP) 38.6079 3.500 1.592014 67.0227 16(ASP) −25.45835.080 17 INFINITY 0.300 1.516798 64.1983 18 INFINITY 0.150 19 INFINITY0.500 1.556708 58.5624 20 INFINITY 1.000 21 INFINITY 0.000

In the zoom lens according to the second embodiment, the both surfacesof the negative lens L11 of the first lens group GR1 (first surface andsecond surface), the both surfaces of the positive lens L21 of thesecond lens group GR2 (sixth surface and seventh surface), the bothsurfaces of the positive lens L31 of the third lens group GR3(thirteenth surface and fourteenth surface) and the both surfaces of thepositive lens L41 of the fourth lens group GR4 (fifteenth surface andsixteenth surface) are non-spherical. Table 6 presents the conicconstants κ and the fourth-order, sixth-order, eighth-order andtenth-order non-spherical coefficients A4, A6, A8 and A10 of thesesurfaces.

TABLE 6 Surface Number κ A4 A6 A8 A10 1 0 −2.80304E−05 3.48626E−07−1.63655E−09 2.42306E−12 2 0 −4.34087E−05 1.42160E−07  1.04665E−09−1.24920E−11  6 0 −5.02623E−05 2.00811E−07 −9.38082E−09 1.97427E−10 7 0 5.26195E−06 4.88591E−07 −5.23925E−09 1.75707E−10 13 0 −8.57280E−041.69717E−05 −1.82000E−07 1.26042E−09 14 0 −1.16374E−03 2.13885E−05−4.59796E−07 3.86935E−09 15 0  2.48695E−06 5.38880E−07 −6.18114E−097.20872E−16 16 0  4.11603E−05 8.30781E−08 −3.54062E−09 −5.10862E−12 

Table 7 presents the focal lengths f, F values Fno and half FOVs ω atthe wide-angle end, at the intermediate focal length and at thetelescopic end in Example 2.

TABLE 7 Wide-Angle Intermediate Telescopic End Focal Length End f 11.00319.632 35.438 Fno 1.855 3.414 5.095 ω 32.986 21.613 12.526

In the zoom lens according to the second embodiment, a spacing D4between the first lens group GR1 and second lens group GR2, a spacingD12 between the second lens group GR2 and third lens group GR3, aspacing D14 between the third lens group GR3 and fourth lens group GR4and a spacing D16 between the fourth lens group GR4 and filter SG varyin zooming between the wide-angle end and telescopic end. Table 8presents the variable spacings with respect to the respective spacingsat the wide-angle end, at the intermediate focal length and at thetelescopic end in Example 2.

TABLE 8 Wide-Angle Intermediate Telescopic End Focal Length End f 11.00319.632 35.438 D4 26.096 10.604 2.750 D12 0.700 1.9537 2.133 D14 5.21011.744 26.173 D16 5.080 4.632 3.931

[Aberration of Zoom Lens]

FIGS. 6 to 8 illustrate aberration diagrams of the zoom lens accordingto the second embodiment of the present technology at infinity focus.FIG. 6, FIG. 7 and FIG. 8 illustrate aberration diagrams at thewide-angle end, at the intermediate focal length and at the telescopicend, respectively. Portions a, portions b and portions c in thesefigures illustrate spherical aberration diagrams, field curvaturediagrams and distortion aberration diagrams, respectively.

In addition, in the spherical aberration diagrams, the solid lines,broken lines and dotted lines indicate values for the d lines (587.6nm), g lines (wavelength of 435.8 nm) and c lines (wavelength of 656.3nm). Moreover, in the astigmatism diagrams, the solid lines and dottedlines indicate values for the sagittal image surfaces and meridionalimage surfaces.

It is apparent from the aberration diagrams that Example 2 attainsexcellent imaging performance, correcting the aberrations favorably.

3. Third Embodiment Lens Configuration

FIG. 9 is a diagram illustrating a lens configuration of a zoom lensaccording to a third embodiment of the present technology. The zoom lensincludes, in order from the object side to the image side, a first lensgroup GR1 having negative refractive power, a second lens group GR2having positive refractive power, a third lens group GR3 having negativerefractive power and a fourth lens group GR4 having positive refractivepower.

The first lens group GR1 includes a double concave-shaped negative lensL11 and a meniscus-shaped positive lens L12 convex to the object side.

The second lens group GR2 includes, in order from the object side to theimage side, a positive single lens L21 convex to the object side and acemented lens configured by joining a double convex-shaped positive lensL22, a double concave-shaped negative lens L23, and a doubleconvex-shaped positive lens L24.

The third lens group GR3 includes a meniscus-shaped negative lens L31convex to the object side.

The fourth lens group GR4 includes a double-convex positive lens L41.

In the zoom lens according to the third embodiment, an aperture stop STOis disposed between the second lens group GR2 and third lens group GR3.The aperture stop STO defines the F value. Moreover, a filter SG isdisposed between the fourth lens group GR4 and an image plane IMG.Furthermore, with a mask pasted on the imaging surface (R2 surface) ofthe negative lens L31 of the third lens group GR3, light rays on thecircumference at the wide-angle end are shielded.

The zoom lens according to the third embodiment has a magnificationfactor of 3.4. In zooming, the first lens group GR1, second lens groupGR2, third lens group GR3 and fourth lens group GR4 are movable.

[Specifications of Zoom Lens]

Table 9 presents data of the lenses in Example 3, in which specificnumerical values are applied to the zoom lens according to the thirdembodiment.

TABLE 9 Surface Curvature Refractive Abbe Number i Radius R Spacing DIndex Nd Number Vd  1(ASP) −110.6651 0.500 1.851348 40.1045  2(ASP)15.3496 4.030  3 23.2119 2.071 2.0027 19.317  4 45.0018 26.354  5(ASP)11.6328 3.150 1.77376 47.167  6(ASP) 89.5151 0.114  7 18.0274 3.7701.83481 42.7207  8 −35.8276 0.860 1.74901 26.3211  9 7.0945 2.099 1014.8808 2.500 1.53600 56.0000 11 −69.3404 0.700 12 INFINITY 0.000Opening Aperture Stop 13(ASP) 15.9495 2.256 1.592014 67.0227 14(ASP)8.598 4.682 15(ASP) 39.6727 3.500 1.592014 67.0227 16(ASP) −27.33085.083 17 INFINITY 0.300 1.516798 64.1983 18 INFINITY 0.150 19 INFINITY0.500 1.556708 58.5624 20 INFINITY 1.000 21 INFINITY 0.000

In the zoom lens according to the third embodiment, the both surfaces ofthe negative lens L11 of the first lens group GR1 (first surface andsecond surface), the both surfaces of the positive lens L21 of thesecond lens group GR2 (fifth surface and sixth surface), the bothsurfaces of the positive lens L31 of the third lens group GR3(thirteenth surface and fourteenth surface) and the both surfaces of thepositive lens L41 of the fourth lens group GR4 (fifteenth surface andsixteenth surface) are non-spherical. Table 10 presents the conicconstants κ and the fourth-order, sixth-order, eighth-order andtenth-order non-spherical coefficients A4, A6, A8 and A10 of thesesurfaces.

TABLE 10 Surface Number κ A4 A6 A8 A10 1 0 −2.33658E−05 2.99644E−07−1.30761E−09 2.24873E−12 2 0 −4.26426E−05 1.89583E−07  5.93809E−11−4.16583E−12  5 0 −5.76019E−05 1.07946E−07 −1.02566E−08 1.59268E−10 6 0−3.27108E−06 3.73169E−07 −5.67274E−09 1.45302E−10 13 0 −4.04314E−042.17415E−06  2.12322E−07 −5.80455E−09  14 0 −6.24948E−04 8.63458E−06−4.88741E−07 1.39341E−08 15 0  2.74349E−05 −7.95024E−07   2.11429E−095.78434E−11 16 0  6.79183E−05 −1.70419E−06   1.00861E−08 4.19559E−11

Table 11 presents the focal lengths f, F values Fno and half FOVs ω atthe wide-angle end, at the intermediate focal length and at thetelescopic end in Example 3.

TABLE 11 Wide-Angle Intermediate Telescopic End Focal Length End f11.001 19.6216 36.991 Fno 1.868 3.1324 5.344 ω 32.848 21.690 12.049

In the zoom lens according to the third embodiment, a spacing D4 betweenthe first lens group GR1 and second lens group GR2, a spacing D11between the second lens group GR2 and third lens group GR3, a spacingD14 between the third lens group GR3 and fourth lens group GR4 and aspacing D16 between the fourth lens group GR4 and filter SG vary inzooming between the wide-angle end and telescopic end. Table 12 presentsthe variable spacings with respect to the respective spacings at thewide-angle end, at the intermediate focal length and at the telescopicend in Example 3.

TABLE 12 Wide-Angle Intermediate Telescopic End Focal Length End f11.001 19.6216 36.991 D4 26.354 10.549 2.743 D11 0.700 2.334 2.200 D144.682 9.764 26.137 D16 5.083 4.770 3.412

[Aberration of Zoom Lens]

FIGS. 10 to 12 illustrate aberration diagrams of the zoom lens accordingto the third embodiment of the present technology at infinity focus.FIG. 10, FIG. 11 and FIG. 12 illustrate aberration diagrams at thewide-angle end, at the intermediate focal length and at the telescopicend, respectively. Portions a, portions b and portions c in thesefigures illustrate spherical aberration diagrams, field curvaturediagrams and distortion aberration diagrams, respectively.

In addition, in the spherical aberration diagrams, the solid lines,broken lines and dotted lines indicate values for the d lines (587.6nm), g lines (wavelength of 435.8 nm) and c lines (wavelength of 656.3nm). Moreover, in the astigmatism diagrams, the solid lines and dottedlines indicate values for the sagittal image surfaces and meridionalimage surfaces. It is apparent from the aberration diagrams that Example3 attains excellent imaging performance, correcting the aberrationsfavorably.

[Summary of Conditional Expressions]

Table 13 presents the values in Examples 1 to 3 according to the firstto third embodiments. It is apparent from the values that theconditional expressions (a) to (d) are satisfied.

TABLE 13 Example 1 Example 2 Example 3 Δm3 1.490 1.433 1.500 fw 11.00411.003 11.001 ft 35.424 35.438 36.991 Conditional Δm3/ 0.075 0.073 0.074Expression (a) (fw × ft)^(1/2) d23_max 2.800 2.800 2.610 Conditionald23_max/ 0.142 0.142 0.129 Expression (b) (fw × ft)^(1/2) f3g −33.556−30.229 −35.452 Conditional f3g/ft −0.947 −0.853 −0.958 Expression (c) L16.258 15.502 3.039 Fno_w 1.855 1.855 1.868 Conditional L × Fno_w 1.5391.456 0.281 Expression (d)

4. Application Example Configuration of Image Capturing Apparatus

FIG. 13 is a diagram illustrating an example of an image capturingapparatus 100 to which the zoom lens according to any of the first tothird embodiments of the present technology. The image capturingapparatus 100 includes a camera block 110, a camera signal processingunit 120, an image processing unit 130, a display unit 140, areader-writer 150, a processor 160, a manipulation acceptance unit 170and a lens driving control unit 180.

The camera block 110 takes on an image capturing function, and includesa zoom lens 111 according to any of the first to third embodiments andan image sensor 112 converting an optical image formed by the zoom lens111 into an electric signal. The image sensor 112 can employ aphotoelectric transducer such, for example, as a CCD (Charge CoupledDevice) and CMOS (Complementary Metal-Oxide Semiconductor). The zoomlens 111 is herein simply illustrated as a single lens, which indicatesthe lens groups according to any of the first to third embodiments.

The camera signal processing unit 120 performs signal processing such asanalog-digital conversion on a captured image signal. The camera signalprocessing unit 120 converts an output signal from the image sensor 112into a digital signal. Moreover, the camera signal processing unit 120performs various kinds of signal processing such as noise reduction,image quality correction, conversion into luminance-chromaticitysignals.

The image processing unit 130 performs recording/playing-back processingof the image signal. The image processing unit 130 performs compressionencoding and decompression decoding of the image signal based on apredetermined image data format and conversion of data specificationssuch as resolution.

The display unit 140 displays the captured image and the like. Thedisplay unit 140 has a function of displaying a manipulation status inthe manipulation acceptance unit 170 and various kinds of data of thecaptured image and the like. The display unit 140 can include, forexample, a liquid crystal display (LCD).

The reader-writer 150 performs access to the memory card 190 whichaccess is writing and read-out of the image signal. The reader-writer150 writes the image data encoded by the image processing unit 130 tothe memory card 190, and reads out the image data recorded in the memorycard 190. The memory card 190 is, for example, a semiconductor memoryremovable to the slot connected to the reader-writer 150.

The processor 160 controls the whole image capturing apparatus. Theprocessor 160 functions as a control processing unit controlling theindividual circuit blocks provided in the image capturing apparatus 100,and controls the individual circuit blocks based on manipulationinstruction signals from the manipulation acceptance unit 170.

The manipulation acceptance unit 170 accepts manipulation from the user.The manipulation acceptance unit 170 can implemented, for example, by ashutter release button for performing shutter operation, a selectionswitch for selecting an operation mode, and the like. The manipulationinstruction signal accepted by the manipulation acceptance unit 170 issupplied to the processor 160.

The lens driving control unit 180 controls driving of the lensesdisposed in the camera block 110. The lens driving control unit 180controls a motor and the like (not illustrated in the figure) fordriving the lenses of the zoom lens 111 based on the control signalsfrom the processor 160.

In standing-by for image capturing, the image capturing apparatus 100outputs the image signal captured by the camera block 110 via the camerasignal processing unit 120 to the display unit 140 under the control ofthe processor 160, and displays it as a camera-through image. Moreover,upon acceptance of the manipulation instruction signal for zooming inthe manipulation acceptance unit 170, the processor 160 outputs thecontrol signal to the lens driving control unit 180, predeterminedlenses in the zoom lens 111 are moved based on the control of the lensdriving control unit 180.

Upon acceptance of the shutter manipulation in the manipulationacceptance unit 170, the captured image signal is outputted from thecamera signal processing unit 120 to the image processing unit 130 toundergo compression encoding and conversion into digital data in apredetermined format. The converted data is outputted to thereader-writer 150 and written in the memory card 190.

Focusing is performed, for example, on the occasions such as a half pushof the shutter release button and a full push thereof for recording(image capturing) in the manipulation acceptance unit 170. In this case,the lens driving control unit 180 moves the predetermined lenses in thezoom lens 111 based on the control signal from the processor 160.

When playing back the image data recorded in the memory card 190, thereader-writer 150 reads out a predetermined image data from the memorycard 190 according to the manipulation accepted by the manipulationacceptance unit 170. Then, after decompression decoding by the imageprocessing unit 130, the image signal to be played back is outputted tothe display unit 140 and the played-back image is displayed.

Incidentally, in the above-mentioned embodiments, a digital still camerais supposed exemplarily as the image capturing apparatus 100, whereasthe image capturing apparatus 100 is not limited to the digital stillcamera but can be widely applied to digital input/output equipment suchas a digital video camera.

As above, according to the embodiments of the present technology, a zoomlens including four lens groups employs a cemented lens configured oftwo out of four lenses in the second lens group, this attaining the zoomlens which is small in dimensions and large in diameter and attainingits excellent optical performance. Namely, the zoom lens and the imagecapturing apparatus according to the embodiments of the presenttechnology employ a zoom ratio of 2.5 to 5, an F value of 2.4 or less atthe wide-angle end, a half FOV of 30° to 40° at the wide-angle endapproximately, this attaining those which are small in dimensions andlarge in diameter and attaining high performance of those.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

Additionally, the present technology may also be configured as below.

(1) A zoom lens including: in order from an object side to an imageside,

-   -   a first lens group having negative refractive power;    -   a second lens group having positive refractive power;    -   a third lens group having negative refractive power; and    -   a fourth lens group having positive refractive power,    -   wherein, in zooming from a wide-angle end to a telescopic end,        the first lens group moves to the object side in a manner that a        distance toward the second lens group narrows, and a distance        between the third lens group and the fourth lens group widens,    -   wherein the third lens group includes a single lens or a single        cemented lens, and    -   wherein the following conditional expressions (a) and (b) are        satisfied,        Δm3/(fw×ft)^(1/2)<0.3  conditional expression (a):        d23_max/(fw×ft)^(1/2)<0.5  conditional expression (b):    -   where    -   Δm3: a variation amount of a distance between the second lens        group and the third lens group in varying magnification, and    -   d23_max: a maximum value of the distance between the second lens        group and the third lens group in varying magnification.        (2) The zoom lens according to (1),    -   wherein the second lens group includes, in order from the object        side, four lenses of a first positive lens, a second positive        lens, a negative lens and a third positive lens, and    -   wherein the second positive lens and the negative lens are        joined with each other.        (3) The zoom lens according to (1) or (2),    -   wherein the third lens group satisfies the following conditional        expression (c),        −3<f3g/ft<−0.8  conditional expression (c):    -   where    -   f3g: a focal length of the third lens group, and    -   ft: a system focal length at the telescopic end.        (4) The zoom lens according to any one of (1) to (3),    -   wherein vibration isolation is performed by moving the third        positive lens or the third lens group perpendicularly to an        optical axis.        (5) The zoom lens according to any one of (1) to (4), including:    -   an aperture stop disposed on the second lens group or between        the second lens group and the third lens group; and    -   a light shielding member shielding a circumferential light ray        on a part of the third lens group at the wide-angle end,    -   wherein the following conditional expression (d) is satisfied,        L×Fno _(—) w/(fw×ft)^(1/2)<2.5  conditional expression (d):    -   where    -   L: a distance along an optical axis between the aperture stop        and the light shielding member at the wide-angle end,    -   Fno_w: an F value at the wide-angle end,    -   fw: a system focal length at the wide-angle end, and    -   ft: a system focal length at the telescopic end.        (6) The zoom lens according to any one of (2) to (4),    -   wherein each of the third positive lens and the third lens group        includes a single lens made of a resin.        (7) The zoom lens according to any one of (1) to (6), further        including a lens having substantially no lens power.        (8) An image capturing apparatus including:    -   a zoom lens including, in order from an object side to an image        side,        -   a first lens group having negative refractive power,        -   a second lens group having positive refractive power,        -   a third lens group having negative refractive power, and        -   a fourth lens group having positive refractive power; and    -   an image sensor converting an optical image formed by the zoom        lens into an electric signal,    -   wherein, in zooming from a wide-angle end to a telescopic end,        the first lens group moves to the object side in a manner that a        distance toward the second lens group narrows, and a distance        between the third lens group and the fourth lens group widens,    -   wherein the third lens group includes a single lens or a single        cemented lens, and    -   wherein the following conditional expressions (a) and (b) are        satisfied,        Δm3/(fw×ft)^(1/2)<0.3  conditional expression (a):        d23_max/(fw×ft)^(1/2)<0.5  conditional expression (b):    -   where    -   Δm3: a variation amount of a distance between the second lens        group and the third lens group in varying magnification, and    -   d23_max: a maximum value of the distance between the second lens        group and the third lens group in varying magnification.        (9) The image capturing apparatus according to (8), further        including a lens having substantially no lens power.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2012-118213 filed in theJapan Patent Office on May 24, 2012 the entire content of which ishereby incorporated by reference

What is claimed is:
 1. A zoom lens comprising: in order from an objectside to an image side, a first lens group having negative refractivepower; a second lens group having positive refractive power; a thirdlens group having negative refractive power; and a fourth lens grouphaving positive refractive power, wherein, in zooming from a wide-angleend to a telescopic end, the first lens group moves to the object sidein a manner that a distance toward the second lens group narrows, and adistance between the third lens group and the fourth lens group widens,wherein the third lens group includes a single lens or a single cementedlens, and wherein the following conditional expressions (a) and (b) aresatisfied,Δm3/(fw×ft)^(1/2)<0.3  conditional expression (a):d23_max/(fw×ft)^(1/2)<0.5  conditional expression (b): where Δm3: avariation amount of a distance between the second lens group and thethird lens group in varying magnification, and d23_max: a maximum valueof the distance between the second lens group and the third lens groupin varying magnification.
 2. The zoom lens according to claim 1, whereinthe second lens group includes, in order from the object side, fourlenses of a first positive lens, a second positive lens, a negative lensand a third positive lens, and wherein the second positive lens and thenegative lens are joined with each other.
 3. The zoom lens according toclaim 1, wherein the third lens group satisfies the followingconditional expression (c),−3<f3g/ft<−0.8  conditional expression (c): where f3g: a focal length ofthe third lens group, and ft: a system focal length at the telescopicend.
 4. The zoom lens according to claim 2, wherein vibration isolationis performed by moving the third positive lens or the third lens groupperpendicularly to an optical axis.
 5. The zoom lens according to claim1, comprising: an aperture stop disposed on the second lens group orbetween the second lens group and the third lens group; and a lightshielding member shielding a circumferential light ray on a part of thethird lens group at the wide-angle end, wherein the followingconditional expression (d) is satisfied,L×Fno _(—) w/(fw×ft)^(1/2)<2.5  conditional expression (d): where L: adistance along an optical axis between the aperture stop and the lightshielding member at the wide-angle end, Fno_w: an F value at thewide-angle end, fw: a system focal length at the wide-angle end, and ft:a system focal length at the telescopic end.
 6. The zoom lens accordingto claim 2, wherein each of the third positive lens and the third lensgroup includes a single lens made of a resin.
 7. An image capturingapparatus comprising: a zoom lens including, in order from an objectside to an image side, a first lens group having negative refractivepower, a second lens group having positive refractive power, a thirdlens group having negative refractive power, and a fourth lens grouphaving positive refractive power; and an image sensor converting anoptical image formed by the zoom lens into an electric signal, wherein,in zooming from a wide-angle end to a telescopic end, the first lensgroup moves to the object side in a manner that a distance toward thesecond lens group narrows, and a distance between the third lens groupand the fourth lens group widens, wherein the third lens group includesa single lens or a single cemented lens, and wherein the followingconditional expressions (a) and (b) are satisfied,Δm3/(fw×ft)^(1/2)<0.3  conditional expression (a):d23_max/(fw×ft)^(1/2)<0.5  conditional expression (b): where Δm3: avariation amount of a distance between the second lens group and thethird lens group in varying magnification, and d23_max: a maximum valueof the distance between the second lens group and the third lens groupin varying magnification.